Filament shield



Mam}! 1959 c. R. MARSH .FILAMENT SHIELD Filed Au 26, 1953 I INVENTOR. CR. M51819,

I ww 2,876,375 FILAMENT SHIELD Charles R. Marsh, Boalsburgh, r5,assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Application August 26, 1953 Serial No.376,556 6 Claims. c1. 31'3-+117) I This invention relates to shields forincandescent filaments and, more particularly, to shields for automobileheadlight incandescent filaments.

Heretofore, shields for automobile headlight incandescent filaments havebeen provided between the filament and the lamp lens to prevent directfilament light from shining into the eyes of oncoming drivers, thuscreating a condition of glare. In addition, automobile headlight lensesare so designed as to receive substantially parallel light, as reflectedby a paraboloidal reflector, and to refract this substantially parallellight into a carefully di rected and distributed beam. To provide such alight source, an incandescent filament is normally centered atapproximately the paraboloidal focus and substantially all light fromthe incandescent filament which strikes the paraboloidal reflector isreflected toward the lamp lens in a substantially parallel beam. I

Since the filament shield is somewhat removed from the filament, andthus the paraboloidal focus, light which is reflected from the filamentshield toward the paraboloidal reflector will appear as though it isemanating from a source which is located olf the paraboloidal focus.This light will thus be re-reflected from the paraboloidal reflector ina scattered manner. This scattered light on striking the lamp lens willoften be refracted toward areas which are not intended to receivesuch'stray light, thus causing undesirable illumination from theautomobile headlight.

To eliminate this undesirable illumination emanating from the filamentshield, it has been customary to provide the filament shield with asurface and coating which will minimize any reflection whilesimultaneously diffusing such light as is reflected, so that theunwanted light reflected from the filament shield will be minimized.Shields of the prior art have been made non-reflecting and difiusing byvarious methods, some of which are sandblasting a nickel-iron shield,blue-oxide coating a nickeliron shield, or acid-etching a nickel-ironshield, which methods are well known in the art. While these methods arerelatively satisfactory, the reflectivity from the generally regularsurface of the filament shield is still too high, the coefficient ofreflection being in the order of 0.1, which, because of the proximity ofthe shield to the filament, results in an undue amount of lightreflected by the filament shield toward the paraboloidal reflector.

It is the general object of the invention to overcome the foregoing andother difliculties of and objections to prior art practices by theprovision of a filament'shield which minimizes filament reflectiontoward the reflector.

Still another object of the invention is the provision of a filamentshield which may utilize the present nonreflecting coatings, whilehaving a reflectivity which is approximately one order of magnitudelower than the reflectivity for the present filament shields.

A further object of the invention is to provide a filament shield whichis economical to manufacture.

The aforesaid objects of the invention and other obtes Pat 2,876,375Patented Mar. 3, 1959 jects which will become apparent as thedescription proceeds, are achieved by providing a filament shield with agenerally serrated or corrugated surface so that most of theincandescent filament: light will be reflected at least twice by theserrated or corrugatedportions of the filament shield before beingfinally reflected towardthe lamp paraboloidal reflector. For a betterunderstanding of the invention, reference should be had to theaccompanying drawings, in which:

Fig. l is a sectional plan view of an automobile head lightincorporating my serrated filament shield;

Fig. 2 is an elevational view of the filament shield taken along thelines 22 of Fig. 1-, in the direction of the arrows; 1

Fig. 3 is a sectional view through Fig. 2, taken along the lines 3-3 inthe direction of the arrows;

Fig. 4 is a fragmentary cross-sectional enlargement of one of theserrations of the filament shield, as shown in Fig. 3, showing howv thedirect light from the filament is reflected from the individual serratedor corrugated portions of the filament shield;

Fig. 5 is a front .elevational view of an alternative embodiment of thefilament shield, which view corresponds to Fig. 2;

Fig. 6 is a sectional view of the alternative embodiment of the filamentshield shown in Fig. 5, taken along the lines VIVI in the direction ofthe arrows;

Fig. 7 is a further alternative embodiment of the filament shield shownin Figs. .2 and ,3, wherein the filament shield has a generally flatconfiguration.

With specific reference to the form of the invention illustrated in thedrawings, the numeral 10 indicates gen erally an automobile lamp havinga hollow paraboloidal reflector. 12, a lens 14 having the generalconfiguration of a hollow spherical sector, sealed to the reflector atits periphery to' form a lamp envelope, and lead-in conductors 16 sealedthrough the back of the reflector 12 and supporting a tungsten or otherrefractory metal filament 18 substantially at the focus of theparaboloidal reflector. The lens and reflector may be fabricated ofpressed glass, as is common in the art, and the inner surface of thereflector is silvered or aluminized to provide the reflecting surface,as, is also common in the art. The lead-in conductors 16 may befabricatedof copper or other conducting material and terminateat one endat the filament l8 and at the other end at lead-in conductor ferrules 20which are sealed through the back of the reflector 12 to facilitatemaking electrical contact between the lead-in conductor and a source ofelectrical energy (not shown).

These ferrules 20 may be fabricated of nickel-iron, if desired, and arewell known in the art; Other'elect'rical contact adapters 22 may beprovided, if desired, to facilitate connecting the source ofelectricalpotential to the lamp lead-in conductor ferrules 20.

Supported between the filament 18 and the lamp lens M is a filamentshield 24 which may have the general configuration of a hollow sphericalsector, so oriented with respect to the lens 14 that the concave sideof. the shield is presented to the filament and the convex sideof theshield is presented to the lens. The filament shield 24 is of such sizeand is located at suchdistance from the filament 18 that a straight linefromlany portion of the filament to any portion of the periphery of thereflecting surface of reflector 12 will be intersected by a portion ofthe shield 24. The shield may be retained in position by a shieldpositioning strap 26 which may be secured between one lead-in conductor16 and the filament shield 24 (as shown) or which may be secureddirectly to the reflector 12. H g

As illustrated in Figs. 2 and 3, the filament shield is preferablycomprised of a series of concentric valleys and ridges which constituteserrations 28. Fig. 4 represents one of the serrations in an enlargedsectional view, and, as illustrated, each serration 28 is substantiallyidentical in configuration and essentially forms an isosceles trianglehaving corners' A, C and B, the corner C being formed by the two sidesof the serration, and the corners A and B being formed by the jointureof the sides ofthe 'serration under consideration with the sides of theadjacent serrations. V V

The angle ACB formed at the vertex of the triangle is important, whichangle is, of course, always less than 180". As is well known fromgeometrical principles, the smaller the angle ACB, the greater thepossibility that any ray oflight striking either side AC or BC will bere-refiected to the other 7 serration side before being finallyreflected toward theparaboloidal reflector 14. The size of the angleACB' which is required to produce multiple reflections, will, of course,.depend upon the distance from the filament to the shield, the radius ofcurvature of the spherical sector shield 24 formed by the series ofconcentric serrations, and the size of the light source. Obviously, ifthe center of the sphere of which the spherical sector forming theshield 24 is a part, coincides with the paraboloidal focus, the angleACB may be made considerably larger and yet provide multiple reflectionsthan if the paraboloidal focus is between the hollow spherical sectorshield 24 and the center of the sphere of which the spherical sectorshield is a part. In the latter case, light would emanate from thefilament 18 toward some of the serrations of shield 24 in a directionother than perpendicular to the base AB or triangle ACB. In this lattercase, as is obvious from geometrical considerations, the smaller theangle ACB, the greater the chances of a multiple reflection within theindividual serrations. For the same reasons, the size of theincandescent filament 18, which is an indication of the amount thefilament extremes are offset from the paraboloidal focus and from theaxis of the shield 24, governs the minimum angle ACB which can beutilized and still achieve multiple reflections between, the serratedsides.

I have eniperically found that for a representative automobile headlamp,ifthe angle ACB is no greater than 90, a sufiicient amount. of lightfrom the filament which strikes the shield 24 will be reflected morethan once among the individual serrations 28 of shield 24 to givesatisfactory results. However, this angle does not represent alimitation, and certainly may be increased for some applications, ifdesired.

By way of example and not by Way of any limitation, one specificembodiment of a lamp embodying my invention isas follows: Glass lensdiameter (lamp envelope evacuated) 5.750". Aluminized glass paraboloidalreflector inner -diameter 5.000. Reflector focal length 0,375", Filamentlength (filament horizontal and centered at the paraboloidal focus)0.200". Distance from center of filament to center of shieldvertex ofcenter serration 0.515". Shield diameter 0.960". Radius of sphere ofwhich hollow spherical sector shield H is a part 1.95 Distance fromcenter of sphere of which hollow spherical sector shield is a part tothe paraboloidal focus 0.66 Angle ACB of individual ser- 0 rationsNumber of serrations in shield (these may be formed by preshsing, or;other well-known 7 ea n1 ues ghield flniitterial t 51 f Nl-Fe alloyon-re ecting rea en 0 Acid-etch (20 7 H2804) for 1 shield inner surfacea M u Then Oxi dine with .NaOH, NaVOz, NaNOs (80-10-10) for 20 min. at290 F.

It is obvious that angle ACB may be varied, if desired, betweenconcentric serrations, utilizing a smaller angle toward the periphery ofthe shield. It is also obvious that manufacturing costs dictate the useof as large an angle ACB as practical, since the shield material is lessstressed and manufacturing costs are reduced where the angle ACBapproaches its maximum permissible value {for the individual lamp. Ihave found that where the angle ACB is less than 15, the manufacturingcosts are somewhat increased without appreciable increased benefits,although for some specialized applications, it might be desirable to useangles smaller than 15.

Operation Even though it is believed the operation of the shield will beapparent from the foregoing description, a brief review thereof is madefor the purpose of summary and simplification. As the direct light fromthe filament strikes one of the sides AC or BC of the serrations, itwill usually be reflectedv toward another of the sides of the serration.Assuming the coefficient of reflection of the shield to be 10- theintensity of the beam which is finally reflected toward the paraboloidalreflector will be 10- times the intensity of the beam originallystriking one of the serrated sides for the first time. x," of course,represents the number of times the beam is reflected from the serratedsides. Thus, in two reflections, assuming the coeficient of reflectionto be l0- the beam will be decreased in intensity 100 times, in threereflections 1000 times, etc.

It will be recognized that the objects of the invention have beenachieved by the provision of a light filament shield which minimizes anyfilament reflection from its surface and which cuts down reflected lightfrom the filament shield at least one order of magnitude from thereflection encountered in shields of the prior art. In addition, myfilament shield may be economically fabricated, by conventionaldie-forming techniques, as are well known.'

As a possible alternative embodiment of my invention, the concentricserrations may be replaced by a series of small individual cones, asrepresented in Figs. 5 and 6, which correspond in view to Figs. 2 and 3.In such an embodiment, the governing design principles are the same asthose utilized in designing the preferred embodiment of my invention.

As another possible embodiment of my invention there is shown, in Fig.7, a filament shield in sectional view corresponding to Fig. 3. Such adesign has the slight cost advantage in that it may be fabricated in asubstantially flat configuration, when viewed from the side. In such adesign, if desired, the angle ACB of the individual serrations which arelocated toward the periphery of the shield maybe smaller than thecorresponding angle of the serrations which are located 7 toward thecenter of the shield, or the angle can be maintained the same butoriented toward the filament.

For purposes of economy of manufacture, the angle ACB may be rounded offto facilitate die-forming. However, in such an embodiment, the overalllight reflected from the shield toward the paraboloidal reflector willbe increased, as compared to the light reflected from the preferredembodiment of my invention.

While in accordance with the patent statutes one best known embodimentof the invention has been illustrated and described in detail, it is tobe particularly understood that the invention is not limited thereto orthereby.

I claim:

1. An automobile headlight comprising a hollow paraboloidal reflectorhaving a periphery and a lens sealed tojsaid reflector at its peripheryto form an envelope, lead-in conductors supporting a filament within anenvelope, a filament shield supported between said filament .and saidlens so that a straight line between any portion of said filament andsaid lens is intersected by said filament shield, said filament shieldbeing comprised of a series of joined concentric serrations to form acomposite serrated body, each of said serrations having two sides whichmeet to form a plurality of vertices, each of said plurality of verticesdescribing an angle smaller than a straight angle, and said angle beingless than 90 and more than 15, and the filament shield serrations facingsaid filament being opaque and highly light absorbing.

2. An automobile headlight as specified in claim 1, wherein saidfilament shield has the substantial general configuration of a sphericalsector having a convex portion and a concave portion, and said shieldbeing so oriented within said envelope that said convex portion of saidshield will be nearest said lamp lens.

3. An automobile headlight comprising a hollow parabolical reflectorhaving a periphery and a lens sealed to said reflector at its peripheryto form an envelope, lead-in conductors supporting a filament Withinsaid envelope, a one-piece opaque and light absorbing filament shieldsupported between said filament and said lens so that a straight linebetween any portion of said filament and said lens is intersected bysaid filament shield, said filament shield being comprised of a seriesof adjacent hollow conical surfaces having vertices, and said shieldbeing so oriented that said vertices will point substantially away fromsaid filament.

4. An automobile headlight comprising a hollow paraboloidal reflectorhaving a periphery and a lens sealed to said reflector at its peripheryto form an envelope, lead-in conductors supporting a filament withinsaid envelope, an oqapue and light absorbing filament shield supportedbetween said filament and said lens so that a straight line between anyportion of said filament and said lens is intersected by said filamentshield, said filament shield being comprised of a series of adjacenthollow conical surfaces having vertices, said shield being so orientedthat said vertices will point substantially away from said filament, andeach of said vertices describing an angle which is less than and morethan 15.

5. An automobile headlight as specified in claim 4, wherein saidfilament shield has the substantial general configuration of a sphericalsector having a convex portion and a concave portion, and said shieldbeing so oriented within said envelope that saidconvex portion of saidshield Will be nearest to said lamp lens.

6. An automobile headlight comprising a hollow paraboloidal reflectorhaving a periphery and a lens sealed to said reflector at its peripheryto form an envelope, lead-in conductors sealed through said envelope, afilament electrically connecting to and supported by said lead-inconductors within said envelope, a onepiece filament shield supportedbetween filament and said lens and so positioned that a straight linebetween any portion of said filament and said lens is intersected bysaid filament shield, said filament shield having such configurationthat the filament shield cross section effected by a plane through saidfilament and perpendicular to and through the center of said filamentshield will appear as a series of connecting lines including anglestherebetween of less than 90 and more than 15, and the portions of saidfilament shield facing said filament being opaque and highly lightabsorbing.

References Cited in the file of this patent UNITED STATES PATENTS1,323,963 Caughrean Dec. 2, 1919 1,621,360 Falge Mar. 15, 1927 1,743,793Muros Jan. 14, 1930 1,751,070 Boots Mar. 18, 1930 2,112,411 SchafinerMar. 29, 1938 2,199,014 Stitt Apr. 30, 1940 2,305,818 Tura Dec. 22, 19422,744,209 Ferguson May 1, 1956

